Motor Protection Relays – ANSI Numbers

Motor protection relays detect electrical, thermal, and mechanical faults using ANSI codes: 49 (thermal overload), 50/51 (phase overcurrent), 50N/51N (earth fault), 46 (unbalance), 47 (phase failure), 48 (locked rotor).

Generator Protection & Control device function

DG set protection includes electrical (differential, overcurrent, negative sequence, voltage/frequency, reverse power, loss of excitation, V/Hz, lockout) and mechanical (oil pressure, temperature, level, locked rotor, start limits) layers for comprehensive safety.

Current Transformer (CT) vs Potential Transformer (PT)

CTs measure current by stepping down high currents (e.g., 400A to 5A) in series, while PTs measure voltage by stepping down high voltages (e.g., 11kV to 110V) in parallel; both enable safe metering and protection.

33kV LINE – RELAYS & ANSI NUMBERS

The primary protection for the 33 kV transmission line incorporates relays such as 50, 51, 50N, 51N, 67, 67N, 79, 46, 27, and 59, providing overcurrent, ground-fault, directional, auto-reclosing, unbalance, and voltage protection. System stability functions include relays such as 81U (under-frequency), 81O (over-frequency), 81R (rate-of-change-of-frequency), and 78, ensuring frequency and power-angle stability.

Directional_Earth_Fault_Relay_67N

Directional earth-fault relay (67N) uses residual current and broken-delta voltage for protection; core-balance CT is preferred in high-impedance grounded systems; RCA sets torque angle relative to polarizing voltage.

Various model of Circuit breakers

Circuit breakers vary by function and application: MCB for overload/short circuit; RCCB for earth leakage; Wi-Fi breaker for smart control; MCCB for higher currents; ELCB (legacy) for shock protection; ACB, VCB, BOCB, SF6, and MPCB serve specific voltage, medium, or motor-protection needs.

Breaker Failure Protection (50BF)

Breaker Failure Protection (50BF) trips adjacent breakers if the primary breaker fails to open after a fault, using trip initiation, auxiliary contact status, and residual current detection.

Protection relay in power system

Relay coordination is a fundamental aspect of power system protection, ensuring that only the faulted section is isolated while the rest of the network continues operating reliably. It is essential for equipment safety, system stability, and minimizing power outages.

Differential relay protection in power system

Differential relay protection safeguards equipment by comparing currents at both ends; it trips the circuit breaker if an internal fault causes current imbalance.

What protections are used with power transmission circuits?

High-voltage circuits use dual independent protection relays (Main1/Main2) for reliability. Protections include instantaneous (e.g., differential, Zone 1 distance, high-stage 67N) and time-delayed (e.g., Zones 2–4 distance, directional ground fault).